When my granddaughter was learning to read she at some point encountered the word mucus. Her dad told her what mucus is, but the pronunciation apparently didn't stick in her brain. One day I was babysitting she and her younger brother. She said, I think I'm getting a cold I have a lot of muckus in my nose. I was going to explain when her brother said, with a look of horror on his little face, "What the HELL is a MUCKUS?"
This is now one of our favorite catch phrases. That D@*%$ muckus.